1-The-Quantum-mechanical-model-of-atom.pptx

Chemistry STEM 12

1. The Quantum mechanical model of atom

2. Models of atomic structure: past to present

3. The bohr model

4. The bohr model The electrons were supposed to move in orbits around the nucleus. (like the planets in the solar system) In this model, electrons occupy orbits that are at fixed energies and radii. Each orbit is assigned an integer quantum number, n . The bigger the orbit, the father the electron is from the nucleus and the higher is its energy with higher quantum number. A specific amount ( called quantum ) energy is required to move from one level to another level. When an electron gains quantum of energy, it moves to a higher energy level, and when it loses the same amount of level. An electron in the lowest energy level where it remain stable is said to be in the ground state, one which is in higher energy level and is more reactive is in excited state . The electron is considered to be a moving object with a momentum moving in a well-defined orbit. However, in order to know the exact path of a moving object, such as the orbit Bohr claims, it is important to know the position and velocity of the particle at the same time.

5. Heisenberg’s uncertainty principle States that it is impossible to know a particle’s momentum and position simultaneously with utmost certainty. The more certain you are with an electron’s momentum, the less certain you will be with regards to its position.

6. Schr ödinger’s model

7. Schr ödinger’s model If an electron within an atom is treated as a wave rather than particle, the various allowable energies could be described by the mathematics of three-dimensional wave behavior. This new view came to be called quantum mechanics (quantum theory + wave mechanics). Schr ö dinger wrote and solve mathematical equations to describe the energy and the location of electrons in atom. The quantum mechanical model presents the electrons as not having exact paths around the nucleus in orbits (as Bohr has postulated) and that they cannot be located precisely within an atom. Using Schr ödinger’s wave mechanics, we can only specify regions around the nucleus of an atom in which there is a large probability of finding the electrons .